Gillian Anderson
Some celebrities who believe in aliens, have usually played believers on television or movies, but not Anderson, who plays Dana Scully, a non-believing FBI agent on The X-Files. Then again, while the actress didn’t necessarily say she believed in aliens, she also claimed that she wouldn’t rule it out.
Source
//www.theguardian.com/film/2012/oct/25/gillian-anderson-x-files-fame